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I can trace my search for consciousness in nonresponsive patients to the moment in 1997 when I met Kate, a young teacher from Cambridge, England, who had lapsed into a coma after a flulike illness. Within a few weeks Kate's doctors had declared her to be vegetative—meaning that although she had sleep-wake cycles, she lacked conscious awareness. Her eyes would open and close, and she would appear to look fleetingly around the hospital room, but she showed no signs of inner life and no responses to prompting by her family or doctors.

I was developing new brain-scanning methods at the University of Cambridge, and David Menon, my colleague there, who is an expert on acute brain injury, suggested that we put Kate into our positron-emission tomography (PET) scanner to see whether we could detect any signs of cognitive activity in her brain. It was a long shot, but we suspected that some of our new brain-imaging approaches just might work. While Kate was inside the machine, we showed her pictures of her friends and family by flashing them on a computer screen, and we looked for any signs of a response from her brain. The results were extraordinary. Not only did her brain respond to the faces, but the pattern of brain activity was strikingly similar to what we and others had seen when showing the faces of loved ones to healthy, aware individuals.